Analysis of voltammograms of quasi-reversible redox systems: transformation to potential program invariant form

A simple procedure has recently been suggested (T. Pajkossy, Electrochem. Comm. 90 (2018) 69) by which various types of voltammograms, above all cyclic voltammograms, pertaining to partially diffusion controlled charge transfer reactions can be analysed. Using this procedure, from voltammograms taken with varied scan-rates or other-than-triangular waveforms two scan-rate independent, hysteresis-free functions can be calculated. One of them is the diffusion-free polarization curve; the other the semiintegrated form of the reversible voltammograms. Here we show the underlying theory in details, along with numerical simulations to highlight important properties of the transformation. The theory opens a new route for the determination of charge- transfer rate coefficients of quasi-reversible redox systems

Applications of Chemometrics‐Assisted Voltammetric Analysis

Electroanalytical techniques consist of the interplay between electricity and chemistry, namely the measurement of electrical quantities, such as charge, current or potential and their relationship to chemical parameters. Electrical measurements for analytical purposes have found a lot of applications including industry quality control, environmental monitoring and biomedical analysis. Chemometrics is the chemical discipline that uses mathematical and statistical methods to design or select optimal procedures and experiments and to provide maximum chemical information by analysing chemical data. The use of chemometrics in electroanalytical chemistry is not as popular as in spectroscopy, although recently, applications of these methods for mathematical resolution of overlapping signals, calibration and model identification have been increasing. The electroanalytical methods will be improved with the application of chemometrics for simultaneous quantitative prediction of analytes or qualitative resolution of complex overlapping responses. This chapter focuses on applications of first-, second- and third-order multivariate calibration coupled with voltammetric data for quantitative purposes and has been written from both electrochemical and chemometrical points of view with the aim of providing useful information for the electrochemists to promote the use of chemometrics in electroanalytical chemistry

MATLAB in electrochemistry: A review

International audienceMATLAB (MATrix LABoratory) is a multi-paradigm numerical computing environment and fourth-generation programming language. MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces and interfacing with programs written in other languages, including C, C ++ , Java, Fortran and Python. Electrochemistry is a branch of chemistry that studies the relationship between electricity, as a measurable and quantitative phenomenon, and identifiable chemical change, with either electricity considered an outcome of a particular chemical change or vice versa. MATLAB has obtained a wide range of applications in different fields of science and electrochemists are also using it for solving their problems which can help them to obtain more quantitative and qualitative information about systems under their studies. In this review, we are going to cast a look on different applications of MATLAB in electrochemistry and for each section, a number of selected articles published in the literature will be discussed and finally, the results will be summarized and concluded

Identification and control of deposition processes

The electrochemical deposition process is defined as the production of a coating on a surface from an aqueous solution composed of several substances. Electrochemical deposition processes are characterized by strong nonlinearity, large complexity and disturbances. Therefore, improving production quality requires the identification of a reasonably accurate model which should be found from data in a reasonable amount of time and with a reasonable computational effort. This identification makes it possible to predict the behavior of unmeasured signals and design a control algorithm to meet the demands of consumers. This thesis addresses the identification and control of the deposition processes. A model for an electrochemical cell that takes into account both electrode interfaces and the activity of ions participating in the deposition process is developed and a method for taking into account uncompensated resistance is proposed. Identifiability of two models, the conventional model and the developed model, is investigated under step and sweep form of applied voltage. It is proven that conventional electrochemical cell model can be identified uniquely using a series of step voltage experiments or in a single linear sweep voltammetry experiment on the basis of the measurements of cell current. The Zakai filtering and pathwise filtering methods are applied to a nonlinear in the parameters electrochemical cell model to estimate the electrode kinetics and mass-transfer parameters of the copper electrodeposition process. In the case of known parameters the feedforward controllers that force the concentration at the boundary to follow the desired reference concentration are designed for the deposition processes. The adaptive boundary concentration control problem for the electrochemical cell with simultaneous parameter identification is solved using the Zakai filtering method. Using such a control, depletion in industrial applications, such as copper deposition baths, can be avoided. An identification method for identifying kinetic parameters and a time-varying mixed potential process of the nonlinear electroless nickel plating model is proposed. The method converts the original nonlinear time-varying identification problem into a time-invariant quadratic optimization problem solvable by conventional least squares

Model-based Experimental Design in Electrochemistry

The following thesis applies an experimental design framework to investigate properties of electron transfer kinetics and homogeneous catalytic reactions. The approach is model-based and the classical Butler-Volmer description is chosen to describe the fundamental electrochemical reaction at a conductive interface. The methodology focuses on two significant design variables: the applied potential at the electrode and mass transport mode induced by physical arrangement. An important problem in electrochemistry is the recovery of model parameters from output current measurements. In this work, the identifiability function is proposed as a measure of correspondence between the parameters and output variable. Under diffusion-limit conditions, plain Monte Carlo optimization shows that the function is globally non-identifiable, or equivalently the correspondence is generally non-unique. However by selecting linear voltammetry as the applied potential, the primary parameters in the Butler-Volmer description are theoretically recovered from a single set of data. The result is accomplished via applications of Sobol ranking to reduce the parameter set and a sensitivity equation to inverse these parameters. The use of hydrodynamic tools for investigating electron transfer reactions is next considered. The work initially focuses on the rotating disk and its generalization - the rocking disk mechanism. A numerical framework is developed to analyze the latter, most notably the derivation of a Levich-like expression for the limiting current. The results are then used to compute corresponding identifiability functions for each of the above configurations. Potential effectiveness of each device in recovering kinetic parameters are straightforwardly evaluated by comparing the functional values. Furthermore, another hydrodynamic device - the rotating drum, which is highly suitable for viscous and resistive solvents, is theoretically analyzed. Combined with previous results, this rotating drum configuration shows promising potential as an alternative tool to traditional electrode arrangement. The final chapter illustrates the combination of modulated input signal and appro- priate mass transport regimes to express electro-catalytic effects. An AC voltammetry technique plays an important role in this approach and is discussed step-by-step from simple redox reaction to the complete EC′ catalytic mechanism. A general algorithm based on forward and inverse Fourier transform functions for extracting harmonic currents from the total current is presented. The catalytic effect is evaluated and compared for three cases: macro, micro electrodes under diffusion control condition and in micro fluidic environments. Experimental data are also included to support the simulated design results

The application of neural networks to anodic stripping voltammetry to improve trace metal analysis

This thesis describes a novel application of an artificial neural network and links together the two diverse disciplines of electroanalytical chemistry and information sciences. The artificial neural network is used to process data obtained from a Differential Pulse Anodic Stripping (DPAS) electroanalytical scan and produces as an output, predictions of lead concentration in samples where the concentration is less than 100 parts per billion. A comparative study of several post analysis processing techniques is presented, both traditional and neural. Through this it is demonstrated that by using a neural network, both the accuracy and the precision of the concentration predictions are increased by a factor of approximately two, over those obtained using a traditional, peak height calibration curve method. Statistical justification for these findings is provided Furthermore it is shown that, by post processing with a neural network, good quantitative predictions of heavy metal concentration may be made from instrument responses so poor that, if using tradition methods of calibration, the analytical scan would have had to be repeated. As part of the research the author has designed and built a complete computer controlled analytical instrument which provides output both to a graphical display and to the neural network. This instrument, which is fully described in the text, is operated via a mouse driven user interface written by the author

Applications and Experiences of Quality Control

The rich palette of topics set out in this book provides a sufficiently broad overview of the developments in the field of quality control. By providing detailed information on various aspects of quality control, this book can serve as a basis for starting interdisciplinary cooperation, which has increasingly become an integral part of scientific and applied research

Improving In Vivo Fast-Scan Cyclic Voltammetric Detection of Neuromodulators

Fast-scan cyclic voltammetry is an electroanalytical technique used to probe neuromodulator signaling dynamics in vivo. The popularity of fast-scan cyclic voltammetry has grown in recent years because of its ability to address various neurobiology research interests in a simple, rapid, sensitive, manner in vivo in real time. However, there still remain challenges associated with the identification and detection of neuromodulators in vivo. Here, the application of principal component regression with residual analysis to in vivo fast-scan cyclic voltammetry data is presented for the first time in a straightforward, non-mathematical context. Changing the estimation of rank from the 99.5% cumulative variance method to Malinowski's F-test better separates relevant information from noise contained in the training set cyclic voltammograms. This allows the residual analysis procedure to function more accurately in determining whether the calibration model was applicable for the unknown data set being predicted. The presence of electrode drift is shown to dramatically alter concentration prediction when it is not included during the construction of the calibration model. Several tools including a residual color plot, the pseudoinverse of the principal component regression calibration matrix, and Cook's distance are shown to successfully improve the accuracy and robustness of training set construction and concentration prediction. In addition, the sensitivity of fast-scan cyclic voltammetry is increased by increasing the scan rate of the applied voltage waveform. Analog background subtraction allows some of the charging current to be neutralized, preventing saturation of the system. The in vitro and in vivo sensitivities are significantly improved, approaching a sub-nanomolar limit of detection. Scanning to a potential of 1.3 V requires waveform modification to maintain the increased sensitivity, but the surface integrity of the carbon-fiber microelectrode is altered. Taken together, these improvements allow for a more sensitive detection scheme and a more robust and accurate quantitation methodology associated with the detection of neuromodulators in vivo with fast-scan cyclic voltammetry.Doctor of Philosoph

Application of computer simulation approaches to study the structure and properties of polymeric systems

The study at the nanoscopic level of the polymeric systems is a keystone for a deeper understanding of their internal structure and properties, not only at nanometric scale but also at macroscopic level. The disciplines involved in this scientific field are diverse, including areas such as chemistry, physics, material science, biology and statistics among others. The aforementioned fields converge in a scientific and technologic central branch called nanotechnology. In the last decades, nanotechnology based on polymeric systems has aroused a great interest among the scientific community, as is clearly evidenced by the huge amount of scientific publications and applications developed within this area. However, the experimental complexity for the development of new devices and the economical limitations devoted to this end are barriers that let us think about the use of alternative approaches in this scientific field. In the face of this endeavors, the application of computer simulation methodologies to must be taken into account. The principal focus of this Thesis is the study at the atomic and molecular level of some polymeric systems through theoretical methodologies based on quantum and classical mechanics formalisms. Such methods allow us to support and understand some chemical and physical observables as well as to analyze and describe these systems at their structural level. Within the framework of the application of the atomic and molecular simulation methodologies, this Thesis could be divided mainly in three main research lines: Conducting Polymers, Polymeric Cation Exchange Membranes, and Dendrimers and Dendronized Polymers The first one focusses on evaluating the detection ability of different conducting polymers when they interact with dopamine or morphine with the final aim of developing a sensor based on these materials. The examination of conducting polymers sensitivity to the analyte detection was carried out via inspection of their ability to form secondary interactions (i.e. weak and strong hydrogen bonds, p-stacking interactions), which was examined using quantum mechanical calculations. Second line is devoted to the application of atomistic molecular dynamics simulation for the investigation of the influence of the electric field strength and the temperature in the dynamical and structural properties of cationic exchange membranes. These investigations were focused on the analysis of hydronium transport mechanism, internal structural rearrangements of the membrane and the characteristics of the hydration shell surrounding the diffused hydronium ions. The last working line of this Thesis is centered on the study at electronic and atomic level of dendritic molecules and dendronized polymers through both quantum and classical mechanics formalisms. The structural properties and molecular interactions occurring in a particular class of dendronized polymers were analyzed. On one side, through a characterization of the inter and intramolecular non bonded interactions of two interacting polymer chains in an attempt to relate atomistic information to the rheological response of these large cylindrical-shape objects. On the other side, studying the internal structure and solvent absorption ability of these systems positively charged and comparing them with their neutral analogues. Finally, studies of both dendrimers and dendronized polymers based on all-thiophene dendrons trough quantum mechanics and molecular dynamics were performed. The electronic properties of symmetric and unsymmetric all-thiophene dendrimers containing up to 45 thiophene rings in neutral and oxidized state was investigated. On the other hand, the internal organization of second and third generation macromonomers and dendronized polymers based on all-thiophene dendrons was studied using density functional theory calculations and classical molecular dynamics simulations, respectively.El estudio a nivel nanoscópico de sistemas poliméricos es un punto clave para la comprensión de su estructura atómica y de sus propiedades, no solamente a escala nanométrica sino también a nivel macroscópico. Las disciplinas involucradas en este campo son diversas e incluyen áreas tales como la química, física, ciencia de materiales y estadística, entre otras. Todos estos campos convergen en una rama científica y tecnológica denominada nanotecnología. En los últimos años, el uso de sistemas poliméricos dentro del campo de la nanotecnología ha suscitado un gran interés dentro de la comunidad científica, tal como queda manifiesto debido al gran número de publicaciones científicas y aplicaciones desarrolladas. Sin embargo tanto el grado de complejidad que implica el desarrollo de nuevos dispositivos dentro de esta disciplina como las limitaciones económicas existentes para estos fines, han hecho que los métodos de simulación molecular sean una herramienta clave para continuar avanzando en esta línea de investigación. El propósito de esta Tesis es el estudio de algunos sistemas poliméricos a nivel atómico y molecular mediante métodos teóricos basados en mecánica cuántica y clásica. Dichos métodos nos han permitido corroborar y entender propiedades físico-químicas a la vez que analizar y describir estos sistemas a nivel estructural. Dentro del marco de la aplicación de métodos de simulación atomístico y molecular, esta tesis puede dividirse en tres líneas de trabajo: Polímeros Conductores, Membranas Poliméricas de Intercambio Catiónico, y Polímeros Dendríticos. En la primera línea se ha evaluado, a partir de estudios cuánticos, la capacidad de detección de diversos polímeros conductores al interactuar con morfina o dopamina; con el objetivo final de desarrollar sensores basados en dichos materiales. Los análisis de sensibilidad de estos polímeros para la detección de dichos analitos se llevaron a cabo mediante el estudio de la capacidad que presentan estos sistemas para formar interacciones secundarias (i.e. puentes de hidrógeno y p-stacking). En segundo lugar se han llevado a cabo estudios atomísticos basados en dinámica molecular para estudiar la influencia de la intensidad del campo eléctrico y de la temperatura en las propiedades dinámicas y estructurales que tienen lugar en membranas de intercambio catiónico. Estas investigaciones se centraron en el análisis de los mecanismos de transporte de los iones hidronio, los cambios sufridos a nivel estructural dentro de la membrana y la caracterización de la capa de hidratación que rodea los a los iones difundidos. La última línea de trabajo está centrada en el estudio tanto a nivel electrónico como atomístico de moléculas dendríticas y polímeros dendronizados mediante mecánica cuántica y clásica. Se llevaron a cabo análisis de las propiedades estructurales así como de las interacciones moleculares que tienen lugar en una clase particular de polímeros dendronizados. Por un lado, mediante la caracterización de las interacciones inter e intramoleculares de dos cadenas poliméricas interpenetradas con el objetivo de establecer la relación existente entre la información atomística obtenida y las propiedades viscoelásticas propias de estos objetos cilíndricos. Por otro lado, mediante un estudio comparativo de estos sistemas en estado neutro y cargado para determinar como la distribución de carga afecta a su estructura interna y a su capacidad de absorción en disolución. Finalmente, se han estudiado dendrímeros y polímeros dendronizados basados en dendrones de tiofeno. Se investigaron propiedades electrónicas de estructuras simétricas y asimétricas de dendrímeros con hasta 45 anillos de tiofeno en estado neutro y oxidado. Además, se analizó la organización interna de macromonómeros basados en dendrones de tiofeno de 2ª y 3ª generación así como de sus correspondientes polímeros mediante cálculos de teoría de funcional de densidad y mediante simulaciones de dinámica molecular, respectivamente.Postprint (published version